1. Field of the Invention
The invention relates to the field of analytical mass spectrometry. Specifically it introduces new apparatus and methods for rapid identification and quantification of target compounds in a mixture by means of selection of a single mass ion beam from the multi-mass ion beam derived from the mixture, and further analyzing the single mass ion beam by controlled collision in a gas cell, followed by mass analysis of the resulting fragment ions and other secondary ions. More specifically, the invention relates to a unique new type of collision cell, which allows analytical and economic advantages over previous embodiments of the mass spectrometry--collisional fragmentation--mass spectrometry concept. Furthermore, the invention relates to new methods of automated apparatus control and data collection.
2. Discussion of the Prior Art
Many versions of ion selection--ion collision--fragment ion mass analysis systems for chemical mixture analysis have been described, for example, in the review article by R. G. Cooks in National Bureau of Standards Special Publication 519, Trace Organic Analysis: A New Frontier in Analytical Chemistry, Proceedings of the 9th Materials Research Symposium, April 10-13, 1978, (Issued April 1979). Most versions use one or another form of magnetic mass spectrometer instrument. More recently, several laboratories have described quadrupole mass spectrometer based systems, for example, R. A. Yost and C. G. Enke writing in Analytical Chemistry, 51, 1251A-1274A (1979). The consistent feature of these systems is the use of three quadrupoles in tandem. The first quadrupole is operated in the normal manner, in which both RF and DC voltages are imposed on the rods, and sufficient resolution (determined by the ratio of DC to peak RF voltage) is chosen to select one ion mass for injection into the second quadrupole. The second quadrupole is operated in a well-known but less usual manner, in which no DC voltage, and only a relatively small RF voltage, is imposed on the rods. In this mode, the quadrupole acts as a high pass mass filter, i.e., the amplitude of the RF voltage determines the lowest mass that can successfully traverse the length of the rods, lower masses being rejected and higher masses being transmitted. In these embodiments of the concept, the collision gas is introduced into the enclosure of the second quadrupole, and the amplitude of the RF voltage is chosen sufficiently small that even the low mass collision fragment ions are transmitted. The third quadrupole, operated in the normal manner, then serves to produce a mass specturm of the collision fragment ions emerging from the second quadrupole.